Method for injection molding metallic materials

ABSTRACT

A method for injection molding a metallic material is disclosed in which an injecting material comprised of a half-solidified metallic material and a molten metallic material is injected into a cavity of a die from an injection cylinder through a gate thereof. A non-product portion remaining at the gate of the die is separated from a product portion while it is still hot. The separated high-temperature non-product portion is press-formed into a billet in the injection cylinder. Utilization of heat from the injecting material in melting the high-temperature billet enables reuse of the non-product portion remained at the gate and reduction of heat energy required in melting the billet.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for injection moldingmetallic materials to obtain a product of desired configuration bysupplying a metallic material contained in an injection cylinder into amold cavity.

[0003] 2. Description of the Related Art

[0004] A typical example of known disk brakes for motor vehicles isshown in cross section in FIG. 32 hereof. As shown in FIG. 32, a diskrotor 503 of the example disk brake 502 is mounted to a drive shaft 500via a hub 501. A peripheral portion of the disk rotor 503 is placed in acaliper 506.

[0005] A wheel 509 is braked by transmitting an oil pressure from a feedflow path 508 to a cylinder, not shown, of the caliper 506 and pressingbrake pads 507, 507 onto a disk portion 505 of the disk rotor 503.

[0006] Since the brake pads 507, 507 are pressed hard onto the diskportion 505 of the disk rotor 503, the disk rotor 503 is required to beformed of a high-strength material.

[0007] On the other hand, in order to reduce the total weight of a motorvehicle, the disk rotor 503 is preferably manufactured of a lightweightmaterial.

[0008] Metal matrix composite material (MMC) materials are well knownfor their high strength and lightweight. For example, employing aluminum(Al) alloy as a metal matrix can save the weight, and adding siliconcarbide (SiC) to Al alloy matrix can realize increase in strength.

[0009] A method for manufacturing the disk rotor 503 from an Al alloymatrix composite material will now be described with reference to FIG.34 hereof.

[0010] Such a method is carried out in a conventional apparatus forinjection molding a metal matrix composite material. An injectioncylinder 515 is brought into communication with a cavity 512 defined bya movable die 510 and a stationary die 511 via a gate 513. A plunger 516is mounted to the injection cylinder 515 so as to be capable of upwardand downward movements, an MMC feeding means 518 is connected to theinjection cylinder 515 via a feed path 517, and a shut-off valve 519 ismounted to an exit side of the feed path 517.

[0011] A shut-off valve 519 is opened and an AL alloy matrix compositematerial is fed from the MMC feeding means 518 into the injectioncylinder 515 as shown by arrow a. The plunger 516 is moved upward asshown by arrow b, and Al alloy matrix composite material is filled intothe cavity 512 through the gate 513. Then, the movable die 510 is movedupward as shown by the arrow c to open the die and the cast product istaken out of the die. The cast product taken out will be describedbelow.

[0012] Reference is made next to FIG. 34 showing a cast product takenout from the die. The cast product 520 is cut into a product portion 521and a non-product portion 522.

[0013] The product portion 521 is a member formed of Al alloy matrixcomposite material molded in the cavity 512 and is to be processed toobtain the disk rotor 503 as shown in FIG. 32.

[0014] The non-product portion 522 is a member formed of Al alloy matrixcomposite material remained at the gate 513 (See FIG. 33).

[0015] The non-product portion 522 remained at the gate 513 is also ofAl alloy matrix composite material obtained by adding SiC grains to Alalloy matrix. Therefore, since Al alloy matrix composite material cannotbe reused as it is, it is necessary to separate SiC grains from Al alloymatrix in order to reuse it. However, such separation is technicallydifficult, and if possible, it costs much. Therefore, the non-productportion 522 is put on a shelf in the existing circumstances and thiscontributes to increase in the cost of the product portion 521 molded byAl alloy matrix composite material (or a metallic material).

[0016] On the other hand, there are products that do not require highstrength among injection molded articles. Since such products are notrequired to contain SiC grains for increasing strength, they may beformed of normal aluminum alloy material (or a metallic material) byinjection molding. Therefore, there is a tendency that they areconsidered to be easily reusable because it is not necessary to separateSiC grains as in the case of Al alloy matrix composite material whenreusing the non-product remained at the gate.

[0017] However, in order to reuse the non-product portion as a moltenmaterial in subsequent injection molding, it is necessary to melt thenon-product portion, which requires much heat energy for melting thenon-product portion. Therefore, in the existing circumstances, thenon-product portion is shelved, thereby contributing to increase in costof the product molded of Al alloy material (metallic material).

[0018]FIG. 35 shows a conventional injection molding apparatus. Theinjection molding apparatus 600 includes an injection apparatus 601opposed to a die 602. A molten metallic material 605 is poured into acavity 604 through a gate 603. When the molten material 605 issolidified in the cavity 604, a disk rotor 608 for the disk brake isobtained.

[0019]FIG. 36 shows an example disk rotor including casting defects. Thedisk rotor 608 is a defective apparatus having a defect that is appearedon an opposite side of the gate 603 (See FIG. 35) as a boundary ofimperfect integrity at the joint due to lowering of the temperature ofthe molten material, that is, cold shuts 606 and scabs 607. In otherwords, referring to FIG. 35, when the molten material 605 is injectedinto the cavity 604 through the gate 603 upwardly at the lower portionand then the molten material 605 collides against the upper portion ofthe cavity 604, the cold shuts 606 and scabs 607 are generated.

[0020] Referring now to FIG. 37A to FIG. 37C, a conventional injectionapparatus will be described.

[0021] In FIG. 37A, a molten metal matrix composite material 703 is fedfrom the molten material feeding apparatus 704 into the injectioncylinder 702 of the injecting apparatus 701.

[0022] In FIG. 37B, the injection cylinder 702 is connected to theforming die 705. The molten material 703 is injected into the cavity ofthe forming die 705 by the plunger 706 moving up and down in theinjection cylinder 702, as shown by the arrow.

[0023] In FIG. 37C, the plunger 706 moves to the upper limit andinjecting operation terminates. After that, when the injected moltenmaterial 703 is solidified in the forming die 705, and the cast product707 is completed.

[0024] However, slugs 708 may enter into the cast product 707, which isa defect of the cast product. The slug 708 is a residue 709 generated bythe oxide of the molten material 703 of metal matrix composite material,and is generated on the surface layer portion 711 of the molten material703 and may adhere to the inner wall surface 712 of the injectioncylinder 702. The adhered residue 709 causes a defect on the castproduct 707 by being mixed in the molten material 703. When the defectis developed, the cast product has to be disposed, which leads tolowering of manufacturing efficiency.

SUMMARY OF THE INVENTION

[0025] It is therefore a first object of the present invention to enablethe reuse of the non-product portion remained at the gate to bring downcosts for injection-molded articles formed of metallic material.

[0026] A second object of the present invention is to provide aninjection apparatus for metal matrix composite material that caneliminate defects of cast product caused by residues.

[0027] According to a first aspect of the present invention, there isprovided a method for injection molding a metallic material in which aninjecting material comprised of a half-solidified metallic material or amolten metallic material is injected into a cavity of a die from aninjection cylinder through a gate thereof, the method comprising thesteps of: taking out a cast product from the die while the cast productis still hot, the cast product having a product portion molded in thecavity and a non-product portion remaining at the gate; separating thenon-product portion from the cast product while the non-product portionis in a state of high temperature; shaping the high-temperaturenon-product portion into a billet; putting the billet into the injectioncylinder; and filling the injecting material into the injection cylinderto cause the billet to melt into the injecting material to thereby readythe billet for a succeeding injection cycle.

[0028] In other words, in the first invention, the non-product portionis shaped into a billet of high temperature, and the billet is melted inthe injection cylinder by the use of heat from the injecting material.By utilizing heat from the injecting material for melting the billet,heat energy required to melt the billet can be reduced. In addition,since the billet is melted while it is in the state of high temperature,heat energy can further be saved. Therefore, the non-product portionremained at the gate can be reused without laying the non-productportion on the shelf.

[0029] Preferably, the step of taking out is carried out while the castproduct is held at a temperature of 400 to 100° C. In this temperaturerange, the cast product is half-solidified sot that it can be taken outfrom the die easily, but has heat that can be utilized as heat energy inmelting the billet.

[0030] As an injecting material, for example, a metallic material in ahalf-solidified state and a metal matrix composite material in a moltenstate are prepared. The respective materials are filled into theinjection cylinder such that the metallic material comes to the plungerside of the injection cylinder, and the metal matrix composite materialcomes to the gate side, so that they can be poured into the cavity inthe order of the metal matrix composite material and the metallicmaterial.

[0031] It is preferable to inject materials into the cavity in thesequence of the metal matrix composite material and the metallicmaterial, because the metal matrix composite material is filled into thecavity and the metallic material remains at the gate. It is thus notnecessary to separate a reinforcing material such as SiC grains from themetal matrix composite material when reusing the non-product portionremained at the gate.

[0032] Desirably, the high-temperature non-product portion is placed inthe injection cylinder and the non-product portion is press-formed intoa billet in the injection cylinder to thereby reduce expenses inpressurizing equipment by effective use of the injection cylinder andthe plunger.

[0033] In addition, the inventors have found through researches toprevent generation of cold shuts and scabs that such cold shuts andscabs are generated mainly by the fact that the molten material getscooled at the portion of the cavity remote from the entrance. Therefore,in order to make the molten material resist getting cooled, theinventors have succeeded in obtaining robust cast products for diskbrakes by increasing the volume of the molten material contained in thepart of the cavity remote from the entrance, and maintaining thetemperature of the molten material flowing at the distance almostconstant.

[0034] According to a second aspect of the present invention, there isprovided an apparatus for molding a disk rotor including a disk-shapedbrake ring portion, a cylindrical hub portion formed integrally with thebrake ring portion and projecting a predetermined distance in onesideward direction, and a lid portion formed integrally with a top endof the hub portion, the apparatus comprising: a forming die including astationary die and a movable die defining a cavity therebetween, theforming die being positioned such that that portion of the cavity forforming the brake ring portion and that portion of the cavity forforming the lid portion are arranged vertically; and the cavity portionfor forming the brake ring portion having an overflow portion forincreasing a volume of the cavity on an upper part thereof so that whena molten metal matrix composite material is poured into the cavityupwardly from below, the molten composite material flows into theoverflow portion past said cavity portion.

[0035] In this molding apparatus, the molten metal matrix compositematerial is injected upwardly from below. Therefore, in the case ofcavities for molding disk rotors, the molten material goes into the diefrom below, separates once to the left and the right, and joins again atthe upper portion. Since the cavity has the overflow portion formed atthe upper portion thereof for the brake ring portion, the volume of thecavity is increased by the overflow portion, and thus the amount of themolten material at the upper portion increases. As a consequence, thetemperature of the top end of the molten material resists lowering, andthus cold shuts and scabs on the cast product of a disc rotor can beprevented from occurring when they are joined at the upper portion.

[0036] In a preferred form, the overflow portion is provided in opposedrelation to one surface of the brake ring portion. This causes thevolume of the overflow portion to be increased so that the moltenmaterial can easily be forced into the cavity.

[0037] The overflow portion may comprise one or more recesses extendingradially from a center of the brake ring portion in the form of agroove. As a result, the inlet port of the overflow portion can beformed between the center side and the outer edge, and thus the volumeof the contained molten material may be increased while reducingresistance applied when flowing into the overflow portion.

[0038] According to a third aspect of the present invention, there isprovided an injection apparatus including a forming die into which amolten metal matrix composite material is poured upwardly from below,the apparatus comprising: an injection cylinder provided vertically; aplunger disposed vertically movably within the injection; a blockextending upwardly from a top end of the plunger and having an outerdiameter smaller than an inner diameter of the injection cylinder, theinjection cylinder having an inner wall surface defining, jointly withan outer peripheral surface of the block, a clearance for accommodatinga residue of the molten metal matrix composite material.

[0039] In this arrangement, since the block is not brought into contactwith the residue attached on the inner wall of the injection cylinder,the block does not scrape off the residue. Therefore, when injecting themolten material, the block can push out the central portion of themolten material that is free of the residue ahead of other portions, andthus the residue can be prevented from getting mixed into the moltenmaterial.

[0040] The block may be detachably secured to the plunger. Morespecifically, the plunger may be formed with a projection on the headportion thereof, while the block is formed with a recess on the lowersurface thereof, so that the projection of the plunger can be detachablyfitted in the recess of the block. As a result, the positioning andmounting of the block with respect to the plunger do not take a lot oftrouble.

[0041] It is desirable that the block is formed of a material harderthan the metal matrix composite material after it is solidified. In thisarrangement, even when an impact is applied by a hammer or the like tothe portion of the cast product corresponding to the gate in order totake out the block adhered to the portion of the solidified cast productcorresponding to the gate after injection is terminated, the block inthe cast product is free from deformation and scratches, whereby theblock can be reused.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Certain preferred embodiments of the present invention will bedescribed in more detail below, by way of example only, with referenceto the accompanying drawings, in which:

[0043]FIG. 1 is a perspective view of a disk rotor manufactured by amethod of injection-molding metal material according to a firstembodiment of the present invention;

[0044]FIG. 2 is a cross sectional view taken along line 2-2 of FIG. 1;

[0045]FIG. 3 is a cross sectional view of a injection molding apparatusfor metal materials, according to the present invention;

[0046]FIG. 4 to FIG. 14 are explanatory views showing a method ofinjection-molding metallic material, according to the first embodimentof the present invention;

[0047]FIG. 15 is a cross sectional view of a disk rotor molded by amethod of injection-molding metallic material, according to a secondembodiment of the present invention;

[0048]FIG. 16 and FIG. 17 are explanatory views showing a method ofinjection-molding metallic material, according to the second embodimentof the present invention;

[0049]FIG. 18 is a view showing an overall arrangement of a moldingapparatus for disk rotors, according to the present invention;

[0050]FIG. 19 is a perspective view of a disk rotor;

[0051]FIG. 20 is a cross sectional view showing a forming die accordingto the present invention;

[0052]FIG. 21 is a perspective view of the forming die shown in FIG. 20;

[0053]FIG. 22 is a perspective view of the disk rotor manufactured bythe forming die according to the present invention;

[0054]FIG. 23A to FIG. 23C are explanatory views showing how a moltenmaterial flows as it is injected into the die;

[0055]FIG. 24A and FIG. 24B are views showing a comparative example andan embodiment of the cast disk rotor, respectively;

[0056]FIG. 25 and FIG. 26 are views showing another embodiment of theforming die;

[0057]FIG. 27 and FIG. 28 are views showing a still another embodimentof the forming die;

[0058]FIG. 29 is a cross sectional view of the die connected to theinjection apparatus of the present invention;

[0059]FIG. 30 is an enlarged cross sectional view of the injectionapparatus shown in FIG. 18;

[0060]FIG. 31A to FIG. 31H are views showing an operation of theinjection apparatus shown in FIG. 30;

[0061]FIG. 32 is a cross sectional view of a typical conventional diskbrake for motor vehicles;

[0062]FIG. 33 is a cross sectional view of a conventional injectionmolding apparatus for a metal matrix composite material;

[0063]FIG. 34 is an explanatory views showing a cast product taken outfrom the die of the molding apparatus shown in FIG. 33;

[0064]FIG. 35 is a schematic view showing a conventional injectionmolding apparatus;

[0065]FIG. 36 is a perspective view of a disk rotor having castingdefects produced by the apparatus of FIG. 35; and

[0066]FIG. 37A to FIG. 37C are explanatory views showing an operation ofa conventional injection apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067] The following description is merely exemplary in nature and is inno way intended to limit the invention, its application or uses.

[0068] As shown in FIG. 1, a disk rotor 10 comprises a cylindrical hubportion 11 and a disk-shaped disk portion 18 integrally molded with thehub portion 11. A hub portion 11 comprises a lid 13 integrally molded onthe outer end of the peripheral wall 12, an opening 14 formed at thecenter of the lid 13, and a plurality of bolt holes 15 and a pluralityof stud holes 16 formed around the opening 14. The bolts (not shown) areinserted through a plurality of bolt holes 15 so that the disk rotor 10is secured to the drive shaft (not shown) with these bolts. The studholes 16 are used for press-fitting studs (not shown) for mounting awheel on the disk rotor 10.

[0069] A disk portion 18 faces toward the brake pad of the caliper (notshown) on which the brake pads are pressed against from both sides.Therefore, the disk portion 18 is required to have high strength and tobe superior in abrasion resistance.

[0070] As shown in FIG. 2, since the hub portion 11 is a portion to bemounted to the drive shaft, it is not required to have high strength andto be superior in abrasion resistance as much as it is for the diskportion 18. Therefore, the hub portion 11 is constructed of Al alloymatrix composite material impregnated with Al alloy. In FIG. 2, the areaE1 of Al alloy matrix composite material impregnated with Al alloy ismarked with diagonal lines.

[0071] The disk portion 18 is required to have high strength and to besuperior in abrasion resistance since the brake pads are pressed againstfrom both sides. Therefore, the disk portion is constructed only of Alalloy matrix composite material. In FIG. 2, the area E2 of Al alloymatrix composite material is reticulated.

[0072] The injection molding apparatus for carrying out a method ofinjection molding according to the present invention is shown in FIG. 3.The injection molding apparatus 20 for a metallic material, shown inFIG. 3, comprises a movable die 21 being capable of upward and downwardmovement; a stationary die 23 forming a cavity 22 with the movable die21; an injection cylinder 25 mounted on the stationary die 23; Al metalfeeding means 34 for feeding Al alloy into the injection cylinder 25;and MMC feeding means 37 for feeding Al alloy matrix composite materialin the injection cylinder 25. The injection cylinder 25 has a plunger 30moving upward and downward therein. The Al alloy feeding means 34 isconnected to the injection cylinder 25 via the Al alloy feed path 35.The Al alloy feed path 35 has a shut-off valve for Al alloy 36 on theexit side 35 a thereof. The MMC feeding means 37 is connected to theinjection cylinder 25 via the MMC feed path 38. The MMC feed path 38 hasa shut-off valve for MMC 39 on the exit side 38 a thereof.

[0073] The stationary die 23 comprises a gate 24 that brings the cavity22 and the inside of the injection cylinder 25 into communication.

[0074] The injection cylinder 25 comprises a heater 26 on the outerperiphery near the upper end with the plunger 30 located at the lowerposition. The top end 25 a of the injection cylinder 25 is fitted in therecess 23 a formed on the lower end portion of the stationary die 23 sothat the gate 24 of the stationary die 23 and the inside of theinjection cylinder 25 are brought into communication with each other.The injection cylinder 25 may be removed from the stationary die 23 bypulling the top end 25 a out from the recessed portion 23 a.

[0075] The plunger 30 is provided in the injection cylinder 25 so as tobe capable of reciprocating motion for forcing Al alloy matrix compositematerial or Al alloy in the injection cylinder 25 through the gate 24into the cavity 22.

[0076] The Al alloy feeding means 34 feed Al alloy in thehalf-solidified state through the Al alloy feeding port 27 of theinjection cylinder 25 into the injection cylinder 25 with the shut-offvalve 36 for Al alloy opened.

[0077] The MMC feeding means 37 feeds Al alloy matrix composite materialin the molten state through the MMC feeding port 28 of the injectioncylinder 25 to the inside of the injection cylinder 25 with the shut-offvalve 39 for MMC opened.

[0078] Referring now to FIG. 4 to FIG. 16, a method of injection-moldingmetal matrix composite material according to the first embodiment willbe described. In these figures, the shut-off valve 36 for Al alloy andthe shut-off valve 39 for MMC are blacked out when it is in the “closed”state.

[0079] In FIG. 4, Al alloy 41 in the half-solidified state is fed intothe injection cylinder 25 through the Al alloy feeding port 27 by the Alalloy feeding means 34 as shown by the arrow (1) with the shut-off valve39 for MMC closed and the shut-off valve for Al alloy 36 opened to fillAl alloy 41 in the half-solidified state on the plunger 30. The fillingamount of Al alloy 41 will be described in conjunction with FIG. 7.

[0080] In FIG. 5, Al alloy matrix composite material 42 in the moltenstate is fed into the injection cylinder 25 via the MMC feeding port 28by the MMC feeding means 37 as shown by the arrow (2) with the shut-offvalve for Al alloy 36 closed and the shut-off valve for MMC 39 opened.

[0081] Then, an injecting material 40 including Al alloy in thehalf-solidified state (half-solidified metallic material) 41 and Alalloy matrix composite material in a molten state (molten metallicmaterial) 42 is filled in the injection cylinder 25. The filling amountof metal matrix composite material 42 will be described in conjunctionwith FIG. 7.

[0082] Making Al alloy 41 in the half-solidified state and Al alloymatrix composite material 42 in the molten state, Al alloy matrixcomposite material 42 may be filled on Al alloy 41 in the separatedstate.

[0083] In FIG. 6, after the shut-off valve for MMC 39 is closed, theplunger 30 is moved upward as shown by the arrow (3) by the operatingmeans (not shown). Then, Al alloy 41 in the half-solidified state movesupward and Al alloy matrix composite material 42 in the molten state isfed through the gate 24 into the cavity 22.

[0084] In FIG. 7, the plunger 30 is moved until it reaches the lowersurface of the stationary die 23. Al alloy matrix composite material 42in the molten state is filled into the disk portion forming portion 22 aof the cavity 22 by filling Al alloy 41 in the half-solidified state inthe gate 24. The area filled with Al alloy matrix composite material 42is reticulated and the area corresponds to the area E2 shown in FIG. 2.Here, the filling amount of metal matrix composite material 42 explainedin FIG. 5 is almost the same amount of the reticulated area. The fillingamount of metal matrix composite material 42 may be changed as needed.

[0085] On the other hand, a part of Al alloy 41 goes into the cavity 22through the gate 24 and thus Al alloy matrix composite material 42 isimpregnated with Al alloy 41. The area 43 of Al alloy matrix compositematerial 42 impregnated with Al alloy 41 is marked with diagonal lines,and this area corresponds to E1 of FIG. 2. Here, the filling amount ofAl alloy 41 described in conjunction with FIG. 4 is almost the sameamount with the area 43 marked with diagonal lines added with the areaof the ate 24. The filling amount of Al alloy 41 may be changed asneeded.

[0086] As a next step, the movable die 21 is moved upward as shown bythe arrow (4) to open the die.

[0087] In FIG. 8, the cast product 45 including the product portion 46molded in the cavity 22 and the non-product portion 47 remained at thegate 24 is taken out from the opened die while it is still hot (as anexample, 400 to 100° C., or the temperature slightly lower than thesolidifying temperature). When the temperature of the cast product 45exceeds 400° C., there is a possibility that the cast product 45 cannotbe taken out from the die in the solidified state. On the other hand,when the temperature of the cast product 45 is lower than 100° C., alarge amount of heat energy is required when melting the non-productportion 47, which is not preferable. Therefore, the temperature of thecast product 45 is determined to be 400 to 100° C., so that heat energyrequired when melting the non-product portion 47 is reduced and that thecast product 45 can be taken out from the die in the solidified state.

[0088] As a next step, the non-product portion 47 is separated inhigh-temperature state from the cast product 45 taken out from the dieto obtain the product portion 46. The product portion 46 is processed toobtain the disk rotor 10 shown in FIG. 2. The plunger 30 moves downwardafter the cast product 45 is taken out from the die as shown by thearrow (5).

[0089] As shown in FIG. 9, the top end 25 a of the injection cylinder 25is pulled out of the recess 23 a by moving the injection cylinder 25downward by the cylinder driving means (not shown) as shown by the arrow(6). Then the injection cylinder 25 is removed from the stationary die23. Thereafter, the injection cylinder 25 is moved laterally as shown bythe arrow (7).

[0090] Then, as shown in FIG. 10, the high-temperature non-productportion 47 is put into the injection cylinder 25 from above theinjection cylinder 25 as shown by the arrow. At the same time, thenon-product portion 47 is heated by the heater 26. There as shown inFIG. 11, the pressurizing plunger 49 is inserted from the top end 25 aside of the injection cylinder 25 as shown by the arrow (8) in a statein which the non-product portion 47 is placed on the upper end surfaceof the plunger 30 of the injection cylinder 25.

[0091] In FIG. 12, the billet 48 is obtained by pressing the non-productportion 47 of high-temperature with the pressurizing plunger 49 and theplunger 30. Then, the pressurizing plunger 49 is moved upward as shownby the arrow (9) and pulled out of the injection cylinder 25.

[0092] As a next step, the injection cylinder 25 is mounted to thestationary die 23 by inserting the top end 25 a of the injectioncylinder 25 into the recess 23 a on the stationary die 23 in reverseorder from the sequence described in conjunction with FIG. 9.

[0093] In FIG. 13, Al alloy 41 in the half-solidified state is fedthrough Al alloy feeding hole 27 into the injection cylinder 25 by theAl alloy feeding means 34 as shown by the arrow with the shut-off valvefor MMC 39 closed and the shut-off valve for Al alloy 36 opened, so thatAl alloy 41 in the half-solidified state is filled on the billet 48.Therefore, the filling amount of Al alloy 41 can be reduced by thevolume of the billet 48 from the filling amount described in conjunctionwith FIG. 4.

[0094] In this way, after filling Al alloy 41 in the half-solidifiedstate into the injection cylinder 25, the billet 48 is melted by heatfrom Al alloy 41 and from the heater 26, and then is mixed into Al alloy41 in the half-solidified state as shown in FIG. 14. Subsequently, Alalloy matrix composite material 42 in the molten state is fed by the MMCfeeding means 37 through the MMC feeding port 38 into the injectioncylinder 25 as shown by the arrow with the shut-off valve for Al alloy36 closed and the shut-off valve for MMC 39 opened to be ready for thenext injection.

[0095] According to a method of injection molding metallic material ofthe first embodiment, injecting materials into the cavity 22 in thesequence of Al alloy matrix composite material 42 and Al alloy 41enables to fill Al alloy matrix composite material 41 in the cavity 22and to leave the Al alloy 41 at the gate 24. Therefore, since it is notnecessary to separate SiC grains from Al alloy matrix composite material42 when reusing the non-product portion 47 remained at the gate 24, theexpense for separating SiC grains can be eliminated.

[0096] The non-product portion 47 is molded and shaped into a billet 48while it is still hot (as an example, 400 to 100° C., or the temperatureslightly lower than the solidifying temperature), and the billet 48 ismelted by the use of heat of the half-solidified Al alloy 41 in theinjection cylinder 25. By utilizing heat from Al alloy 41 for meltingthe billet 48, heat energy required for melting the billet 48 may bereduced.

[0097] Since the billet 48 is melted while it is still hot in the firstembodiment, heat energy can further be saved and thus the non-productportion 47 can be reused without putting on the shelf, thereby reducingcosts for the product portion 46 (or disc rotor 10).

[0098] In addition, the non-product portion 47 of high-temperature isput into the injection cylinder 25 and the non-product portion 47 ispressed into a billet 48 with the plunger 30 in the injection cylinder25. Therefore, the injection cylinder 25 and the plunger 30 can beutilized effectively, thereby reducing equipment expenses for pressingoperation. Accordingly, the cost of the product portion 46 can furtherbe reduced.

[0099] When the non-product portion 47 is pressed into a billet 48outside of the injection cylinder 25, it is necessary to transport thenon-product portion 47 to the pressing equipment (not shown), and thenafter pressing, it is necessary to transport to the injection cylinder25. Since it takes a lot of trouble in transportation, which resistsimprovement of productivity. However, according to the first embodimentof the present invention, by pressing into the billet 48 in theinjection cylinder 25, it can save labor for transportation and thusproductivity can be improved.

[0100] In addition, the billet 48 obtained by pressing the non-productportion 47 is placed on the upper surface of the plunger 30 in a firstplace, and Al alloy 41 is filled and heated thereon, and then Al alloymatrix composite material 42 is filled in the injection cylinder 25.Therefore, Al alloy 41 in the half-solidified state including moltenbillet 48 is not forced into the cavity 22 but remains at the gate 24when performing injection molding. As a consequent, even if the billet48 contains impurities, they cannot be mixed in the product portion 46.

[0101] Now, a method of injection molding according to the secondembodiment will be described. FIG. 15 is a disk rotor formed by a methodof injection-molding metallic material according to the secondembodiment.

[0102] The disk rotor 50 comprises, as in the case of the firstembodiment, a cylindrical hub portion 51, and a disk-shaped disk portion54 integrally formed with the hub portion 51. The hub portion 51 and thedisk portion 54 are formed only of Al alloy matrix composite material.

[0103] Referring now to FIG. 16 and FIG. 17, a method ofinjection-molding metal matrix composite material according to thesecond embodiment will be described.

[0104] In FIG. 16, as in the first embodiment, Al alloy 41 in thehalf-solidified state and Al alloy matrix composite material 42 in themolten state are fed into the injection cylinder 25 by the Al alloyfeeding means 34 and the MMC feeding means 37, and then the shut-offvalve for Al alloy 36 and the shut-off valve for MMC 39 are closed asshown in the figure. In this case, the filling amount of Al alloy 41 issmaller than that described in the first embodiment, and the fillingamount of metal matrix composite material 42 is larger than thatdescribed in the first embodiment.

[0105] Then, the plunger 30 is moved upward until it reaches to thelower surface of the stationary die 23. By filling Al alloy 41 in thehalf-solidified state into the gate 24, Al alloy matrix compositematerial 42 in the molten state is filled into the cavity 22. The areafilled with Al alloy matrix composite material 42 is reticulated.

[0106] On the other hand, a part of Al alloy 41 is forced from the gate24 into the cavity 22 and thus Al alloy matrix composite material 42 isimpregnated with Al alloy 41. The portion with diagonal lines representsthe area 43 of Al alloy matrix composite material 42 impregnated with Alalloy 41.

[0107] Subsequently, the movable die 21 is moved upward to open the dieas shown by the arrow.

[0108] The cast product 55 is taken out of the opened die as shown inFIG. 17, and the non-product portion 57 of the cast product 55 is cutoff the product portion 56. The disk rotor 50 is obtained by processingthe product portion 56. Since the portion 52 of Al alloy contained inthe product portion 56 is small, it is removed when the product portion56 is processed.

[0109] On the other hand, since the non-product portion 57 is formedonly of Al alloy, it can be reused. Therefore, as in the firstembodiment, the cost of the disk rotor 50 can be reduced.

[0110] In the first and second embodiment described above, metal matrixcomposite material 42 employed is Al alloy matrix composite materialobtained by adding SiC grains to Al alloy matrix. However, it is alsoapplicable to employ metal matrix composite material comprising a matrixformed of other metal materials and a reinforcing material (such as SiCor alumina) in the state of fibers, grains or a plate contained therein.

[0111] In addition, in the first and the second embodiment, a method ofmolding a high strength disk rotor 10 by filling Al alloy matrixcomposite material 42 in the molten state in the cavity 22 and leavingAl alloy 41 in the half-solidified state at the gate 24 is described asan example. However, the method of injection molding a metallic materialaccording to the present invention may be applied to the case where theproduct is formed only of Al alloy 41 or other metal material byinjection molding.

[0112]FIG. 18 shows an injection molding apparatus for disk rotors shownin the schematic diagram.

[0113] The injection molding apparatus 100 for disk rotors comprises amolten material filling apparatus 112 placed on the stand 111, and amolding apparatus 113. The molding apparatus 113 comprises a die 114.The reference numeral 115 designates a molten material feeding apparatusfor feeding the molten material 124 such as metal matrix compositematerial into the molten material filling apparatus 112.

[0114] The molten material filling apparatus 112 comprises atransporting apparatus 121, a hoisting apparatus provided on thetransporting apparatus 121, and a injection apparatus 123 mounted on thehoisting apparatus. The molten metal matrix composite material 124 isinjected in the cavity 151 of the die 114 from the injection apparatus123.

[0115] The transporting apparatus 121 moves the hoisting apparatus 122and the injection apparatus 123 toward the side of the molten materialfeeding apparatus 115 (in the direction shown by the arrow (1)) as shownby a phantom line, and the molten material 124 fed from the moltenmaterial feeding apparatus 115 is transported (in the direction shown bythe arrow (2)). The hoisting apparatus 122 moves upward as shown by aphantom line (in the direction shown by the arrow (3)) to connect theinjection apparatus 123 with the die 114, and moves downward after theinjection apparatus 123 injected the molten material 124.

[0116] The molding apparatus 113 comprises a die mounting board 125(stationary board 125 a, movable board 125 b) for mounting the die 114,a tie bar 126 for supporting the die mounting board 125, a cylinder 127for opening and closing the die 114, and a toggle link mechanism 128. Inthis example, opening and closing of the die 114 is made in the lateral(horizontal) direction. The movable board 125 b moves in the die openingdirection (in the direction shown by the arrow (4)) as shown in aphantom line to open the die 114, and the cast disk rotor is taken outby the takeoff apparatus (not shown).

[0117]FIG. 19 is a perspective view of the disk rotor manufactured bythe molding apparatus according to the present invention. The diskroller 130 comprises a brake ring portion 131 as a disk-shaped diskportion, and a cylindrical hub portion 135 formed integrally with thebrake ring portion 131 and extending outwardly. The hub portion 135comprises a lid portion 132 on the projected outer end thereof. The lidportion 132 is formed with an opening at the center thereof. The hubportion 135 projects by a constant distance L from the outer surface 136of the brake ring portion 131 to the outer surface of the lid portion132.

[0118]FIG. 20 and FIG. 21 show a die. The die 114 comprises a stationarydie 141 and the movable die 142. The stationary die 141 is formed with astationary side die surface 143. The stationary side die surface 143 isformed with an overflow portion 144 on the upper side thereof. Thestationary side die surface 143 is formed with a gate 145 connecting tothe die surface 43 at the lower portion thereof. Two pin holes 146, 146(See FIG. 21) for positioning are formed on the stationary die 141. Themovable die 142 is formed with a movable side die surface 147. Themovable die 142 is formed with a gate 148 connecting to the movable sidedie surface 147 at the lower portion thereof. The positioning pins 149,149 for fitting into the pin holes 146, 146 are provided on the movabledie 142. The stationary side die surface 143 and the movable side diesurface 147 define a cavity 151 of the die 114. The die 114 is a castdie with an overflow portion 144 evaginated on the upper portion 152 ofthe cavity 151 so that the cavity 151 is oriented in the verticaldirection. The reference numeral 153 designates a parting line.

[0119] In FIG. 21, the reference numeral 155 designates a partingsurface of the stationary die 141, and the reference numeral 156designates the parting surface of the movable die 142.

[0120] The stationary side die surface 143 comprises a stationary sidedie surface for rings 161 for forming brake ring portions 131 (See FIG.19), a stationary side die surface for hubs 162 for forming the hubportions 135, and a stationary side die surface for lids 163 for formingthe lid portions 132 (See FIG. 19). The movable side die surface 147comprises a movable side die surface for rings 164 for forming the brakering portions 131, a movable side die surface for the hubs 165 forforming hubs 135, and a movable side die surface for the lids 166 forforming the lid portions 132. In other words, the cavity 151 for formingthe brake ring portions 131 (See FIG. 20) is defined by the stationaryside die surface for rings 161 and a movable side die surface for rings164, and the cavity 151 for forming lid portions 132 (See FIG. 19) isdefined by the stationary side die surface for lids 163 and the movableside die surface for lids 166.

[0121] The overflow portion 144 comprises a plurality of recesses 171,172, 173, 174, 175 extending radially from the center 176 of the die inthe shape of grooves on the upper portion of the stationary side diesurface for rings 161.

[0122]FIG. 22 is a perspective view of the disk rotor formed of a castproduct manufactured by the use of the molding apparatus of the presentinvention. The cast product 177 of the disk rotor is formed with aplurality of rib-shaped projections 179 radially extending from thecenter 181 of the brake ring portion 131 on the outer surface 136thereof by the overflow portion.

[0123] The operation of the disk rotor molding apparatus described abovewill now be described.

[0124]FIG. 23A to FIG. 23C are views showing the operation of the diskrotor molding apparatus according to the present invention, in which theflow of the molten material 124 in the cavity 151 is shown in aschematic form. (a) shows side views of the stationary die 114, and (b)shows interior elevations thereof.

[0125] In FIG. 23A (a), the molten metal matrix composite material 124is injected into the die 114 upwardly from below by means of theinjection apparatus 123. The molten material 124 branches off to theleft and the right and flows in the cavity 151 as shown by the arrows(5), (5). At the same time, when it flows in the cavity 151 shown in(b), the cooling action works on the top ends 183, 183 of the moltenmaterial 124.

[0126] In FIG. 23B(a) and (b), the molten material 124 flows in thecavity 151 as shown by the arrows (6),(6), and goes into the overflowportion 144. Since the volume of the flow path (cavity 151) is increasedby the recesses 171, 172 of the overflow portion 144 to increase theamount of the molten material 124, the top ends 183, 183 resistslowering in temperature. In addition, increase in the volume of the flowpath (cavity 151) alleviates resistance acting on the molten material124 and prevents retention of the molten material 124.

[0127] As shown in FIG. 23C(a) and (b), the top ends 183, 183 of themolten material 124 are further forced into the overflow portion 144. Inother words, the recesses 173, 174 of the overflow portion 44contributes to increase in the volume of contained molten material,thereby contributing to heat-retention and to prevention of retention.

[0128] When the molten material 124 goes into the recess 175 at thecenter of the overflow portion 144, and then the top ends 183, 183 ofthe molten material 124 are joined with each other, the top ends 183,183 are pressed against each other to melt the joint 184 completely.Therefore, occurrence of cold shuts and scabs can be prevented.

[0129] Providing the overflow portion 144 so as to face toward the outersurface 136 of the brake ring portion 131 can increase the crosssectional area of the inlet port 185 of the overflow portion 144. As aconsequent, resistance of inflow of the molten material into theoverflow portion 144 is reduced, and simultaneously, the volume ofcontained molten material is increased, thereby resisting lowering intemperature of the molten material 124.

[0130] In addition, since the overflow portion 144 extends radially fromthe center 181 of the brake ring portion 131 in the state of grooves,the inlet port 185 of the overflow portion 144 opens from the center 181side toward the edge 186 side. As a consequent, the volume of thecontained molten material between the center 181 side and the edge 186side increases, whereby the temperature of the molten material from thecenter 181 side to the edge 186 side resists lowering, and thus the topends 183, 183 of the molten material 124 can be molten completely.Therefore, cold shuts and scabs can completely be prevented.

[0131] Since the overflow portion 144 extends radially from the center181 of the brake ring portion 131 in the state of grooves, theprojections 179 (See also FIG. 2) formed by the overflow portion 144 canbe cut off simultaneously with the cutting operation of the brake ringportion 131 (See also FIG. 19), so that the projection 179 can easily beremoved.

[0132] Since the overflow portion 144 extends radially from the center181 of the brake ring portion 131 in the state of grooves, the sameeffect can be expected even when the position of the joint between thetop ends 183, 183 of the molten material 124 changes. In other words,the joint 184 of the molten material 124 is not necessarily formed inthe recess 175, but the same effect can be achieved between the recess171 and the recess 175 even when the position of the joint 184 varies.

[0133]FIG. 24A and FIG. 24B are comparative views of cast disk rotors.

[0134]FIG. 24A shows a disk rotor 108 formed by the disk rotor moldingapparatus in the related art with cold shuts 106 and scabs 107 generatedthereon.

[0135]FIG. 24B shows a disk rotor 130 formed by the disk rotor moldingapparatus according to the present invention. As shown in the figure,cold shuts 106 and scabs 107 are not generated by the molding apparatusaccording to the present invention.

[0136] Another embodiment of the disk rotor molding material accordingto the present invention will be described referring to FIG. 25 and FIG.26.

[0137]FIG. 25 is a cross sectional view of the principal portion of thedie 214. The die 214 (stationary die 241, movable die 242) has anoverflow portion 244 above the cavity 251 in communication with theouter edge 288 of the cavity 251. The reference numerals 245 and 248designate a gate.

[0138]FIG. 26 is a view of the movable die 242 shown in FIG. 25, takenalong the line 26-26. The overflow portion 244 is constructed of aplurality of trough-shaped recesses 291 formed on the parting surface256 of the movable die 242, and likewise, trough-shaped recesses 292formed on the stationary die 241 (See FIG. 25).

[0139] As shown in the figure, since the overflow portion 244 isprovided above the cavity 251 in communication with the outer edge 288of the cavity 251, air pressed by the molten material is flown into theoverflow portion 244, and thus the molten material pressurizes air inthe overflow portion 244. As a consequent, the volume of the containedmolten material increases, and thus the lowering of the temperature isprevented. In addition, since air does not stay in the cavity 251, topends of the molten materials are positively brought into contact witheach other, so that the top ends of the molten materials are meltedtogether. Therefore, occurrence of cold shuts and scabs can beprevented.

[0140] Referring now to FIG. 27 and FIG. 28, still another embodiment ofthe present invention will be described.

[0141]FIG. 27 is a cross sectional view of the principal portion of thedie 314. The die 314 (stationary die 341, movable die 342) comprisesheating means, such as heaters 394, 395 at the positions near the upperportion of the cavity 351. Heater holes 396, 397 are formed atprescribed distances S, S away from the cavity 351, and cartridgeheaters 398, 398 are fitted in the heater holes 396, 397. The referencenumerals 345 and 348 designate a gate.

[0142]FIG. 28 is a cross sectional view taken along the line 28-28 inFIG. 27. The heater 394 comprises three cartridge heaters 398, 398, 398provided at prescribed pitches P. The heater 395 has the same structureas the heater 394, and thus the description is omitted.

[0143] As shown in the figure, since three cartridge heaters 398 areprovided at the positions near the upper positions of the cavity 351,lowering of the temperature at the top end of the molten material can beprevented. Therefore, occurrence of cold shuts and scabs can beprevented. In addition, since the space to be filled with the moltenmaterial is only the gate 345, 348 except for the cavity 351, the volumeis small, and thus the material can be saved and efficiency of cuttingoperation is increased.

[0144] There may further be provided an overflow portion 144 shown inFIG. 21 according to the embodiment of the present invention on the diesurface for forming the lid portion 132.

[0145] In addition, the recesses 171 to 175 on the overflow portion 144may be continued to form a large recess. The overflow portion 144 shownin FIG. 21 and the overflow portion 244 shown in FIG. 25 and FIG. 26 maybe combined.

[0146] The disk rotor molding apparatus is not limited to the disk rotormolding apparatus 100 shown in FIG. 18. For example, the mechanism otherthan the toggle link mechanism 128 may be employed, and the pipingsystem may be employed in the molten material supplying apparatus 115.In addition, a electric motor may be employed in addition to theclamping cylinder 127.

[0147] An embodiment of the injection apparatus according to the presentinvention will be described now.

[0148]FIG. 29 shows a die to be connected with the injection apparatusof the present invention. The die 414 comprises a stationary die 431 anda movable die 432. The stationary die 31 comprises a stationary side diesurface 433 and a gate 434 formed in communication with the die surface433. The movable die 32 comprises a movable side die surface 435 and agate 436 formed in communication with the die surface 435. The cavity437 of the die 414 is defined by the stationary side die surface 433 andthe movable side die surface 435. The reference numeral 438 designates across gate, which is a passage for the molten material connectingbetween the cavity 437 and the gate 434, 436. The injection apparatus123 shown in FIG. 18 is connected to the die 414 by being fitted in thegate 434, 436. The reference numeral 441 designates an injectioninterface.

[0149] The injection apparatus 123 shown in FIG. 18 is shown in crosssection in FIG. 30 in detail. The injection apparatus 123 comprises aninjection cylinder 446 for storing a prescribed amount of the moltenmaterial upon reception thereof, a plunger 447 moving upward anddownward in the injection cylinder 446 for pushing the molten materialout, and a block 448 detachably mounted on the plunger 447.

[0150] The injection cylinder 446 comprises an inner wall surface 452defined by the prescribed inner diameter D1.

[0151] The plunger 447 comprises a head portion 453 in slide contactwith the inner wall surface 452 of the injection cylinder 446. The headportion 453 comprises a pushing surface 454 for pushing the moltenmaterial on the upper surface thereof, and a trapezoid projection 455projecting upward for supporting the block 448.

[0152] The block 448 comprises an upper surface 461, the outerperipheral surface 462, and a lower surface 463. The lower surface 463is formed with a tapered recess 464. The outer diameter of the block 448is represented by D2. The outer diameter D2 is determined to be smallerthan the inner diameter D1 of the injection cylinder 446, so that aprescribed clearance S is formed. More specifically, the outer diameterD2 has a relation D2=D1-2×S, and determined to be small so as not tocome into contact with residue attached on the inner wall surface 452 ofthe injection cylinder 446.

[0153] Referring now to FIG. 31A to FIG. 31H, the operation of theinjection apparatus according to the present invention will bedescribed.

[0154] In FIG. 31A, the molten metal matrix composite material 424 isfed to the injection cylinder 446 of the injection apparatus 123 by themolten material feeding apparatus 115 (See FIG. 18). This feedingoperation generates a slug 466 in the molten metal matrix compositematerial 424. The slug 466 is a residue 467 generated from an oxide ofthe molten metal matrix composite material 424, which is generated inthe surface layer portion 468 of the molten material 424 and is attachedon the inner wall surface 452 of the injection cylinder 446.

[0155] After the molten material 424 is fed, the injection cylinder 446is moved upward as shown by the arrow (5), so that the upper end surfaceof the injection cylinder 446 is brought into intimate contact with theinjection interface 441 of the die 414 as shown by a phantom line.

[0156] In FIG. 31B, after the injection cylinder 446 is fitted in thedie 414, the injection starts. In other words, when the plunger 447 inthe injection cylinder 446 is moved upward as shown by the arrow (6) topush the molten material 424 out, the molten material 424 is forced intothe cross gate 438 and the cavity 437.

[0157] In FIG. 31C, when the plunger 447 is moved further upward tocontinue injection of the molten material 424, the plunger 447 movesupward while scraping the residue 467 adhered to the inner wall surface452 of the injection cylinder 446. However, since the block 448 has asmall diameter so that it does not brought into contact with the residue467 adhered to the inner wall surface 452 of the injection cylinder 446,the residue 467 is not scraped. As a consequent, the block 448 can pushthe center portion of the molten material 424 that has no residue 467therein. The residue 467 scraped by the plunger 447 stays in theclearance S, so that it is not mixed in the center portion of the moltenmaterial 424.

[0158] In FIG. 31D, when the plunger 447 reaches a prescribed stroke andinjection of the molten material 424 is completed, the scraped residue467 stays in the injection cylinder 446 and stops at the position nearthe cross gate 438. Therefore, it is not flown into the cavity 437.

[0159] After the molten material 424 is solidified, the plunger 447 islowered as shown by the arrow (7). Since the block 448 is detachablyplaced on the head portion 453 of the plunger 447, when the plunger 447moves downward, the block 448 is easily separated from the plunger 447,and the block 448 stays at the portion 472 of the cast product 471corresponding to the gate.

[0160] In FIG. 31E, in order to take the cast product 471 out from thedie 414, the injection apparatus 123 is moved downward as shown by thearrow (8), and then the movable die 432 of the die 414 is moved in thedirection shown by the arrow (9) to open.

[0161] In FIG. 31F, the portion 472 of the cast product 471corresponding to the gate is hit by the hammer 480 or the like to removethe block 448 from the portion 472 of the cast product corresponding tothe gate. The hardness of the block 448 is higher than that of metalmatrix composite material after it is solidified, no deformation orscratch is occurred even when an impact is applied to the block 448.

[0162]FIG. 31G shows a block 448 that is just taken out from the die.Since the block 448 has no deformation or scratch, it can be usedrepeatedly, thereby reducing the production cost.

[0163] In FIG. 31H, the block 448 is placed again on the head portion453 of the plunger 447 of the injection apparatus 123. In this case,since the recess 464 of the block 448 is fitted on the projection 455 ofthe head portion 453, the block 448 can precisely positioned thereon andthus the clearance S can be established.

[0164] In the injection apparatus of the present invention, the examplein which the block 448 is placed on the plunger 447 shown in FIG. 30 isshown as an embodiment. However, the plunger 447 and the block 448 maybe integrally formed.

[0165] While the projection 455 of the plunger 447 is fitted with therecess 464 of the block 448, it is not limited to the projection 455 andthe recess 464. It may be the hole and the pin to be fitted.

[0166] The configuration of the cavity 437 of the die 414 is just shownas an example, and thus it is not limited thereto in the presentinvention.

[0167] Obviously, various minor changes and modifications of the presentinvention are possible in the light of the above teaching. It istherefore to be understood that within the scope of the appended claims,the invention may be practiced otherwise than as specifically described.

What is claimed is:
 1. A method for injection molding a metallicmaterial in which an injecting material comprised of a half-solidifiedmetallic material or a molten metallic material is injected into acavity of a die from an injection cylinder through a gate thereof, saidmethod comprising the steps of: taking out a cast product from said diewhile said cast product is still hot, said cast product having a productportion molded in said cavity and a non-product portion remaining atsaid gate; separating said non-product portion from said cast productwhile said non-product portion is in a state of high temperature;shaping said high-temperature non-product portion into a billet; puttingsaid billet into said injection cylinder; and filling the injectingmaterial into said injection cylinder to cause said billet to melt intothe injecting material to thereby ready the billet for a succeedinginjection cycle.
 2. A method for injection molding a metallic material,as set forth in claim 1, wherein said step of taking out is carried outwhile said cast product is held at a temperature of 400, to 100° C.
 3. Amethod for injection molding a metallic material, as set forth in claim1, further comprising the steps of: preparing a metallic material in ahalf-solidified state and a metal matrix composite material in a moltenstate for serving as the injecting material; filling said metallic andmetal matrix composite materials into said injection cylinder such thatsaid metallic material is positioned closely to a plunger of saidinjection cylinder and said metal matrix composite material ispositioned closely to said gate, so that said materials are injectedinto said cavity in a sequence of said metal matrix composite materialand said metallic material.
 4. A method for injection molding a metallicmaterial, as set forth in claim 1, wherein said high-temperaturenon-product portion is disposed in said injection cylinder so that saidnon-product portion is press-formed into said billet in said injectioncylinder.
 5. A method for injection molding a metallic material, as setforth in claim 4, wherein said non-product portion is press-formed at atemperature of 400 to 100° C.
 6. An apparatus for molding a disk rotorincluding a disk-shaped brake ring portion, a cylindrical hub portionformed integrally with said brake ring portion and projecting apredetermined distance in one sideward direction, and a lid portionformed integrally with a top end of said hub portion, said apparatuscomprising: a forming die including a stationary die and a movable diedefining a cavity therebetween, said forming die being positioned suchthat that portion of said cavity for forming said brake ring portion andthat portion of said cavity for forming said lid portion are arrangedvertically; and said cavity portion for forming said brake ring portionhaving an overflow portion for increasing a volume of said cavity on anupper part thereof so that when a molten metal matrix composite materialis poured into said cavity upwardly from below, said molten compositematerial flows into said overflow portion past said cavity portion. 7.An apparatus as set forth in claim 6, wherein said overflow portion isprovided in confronting relation to one side surface of said brake ringportion.
 8. An apparatus as set forth in claim 7, wherein said overflowportion comprises one or more recesses extending radially from a centerof said brake ring portion and provided in the form of a groove.
 9. Aninjection apparatus including a forming die into which a molten metalmatrix composite material is poured upwardly from below, said apparatuscomprising: an injection cylinder provided vertically; a plungerdisposed vertically movably within said injection; a block extendingupwardly from a top end of said plunger and having an outer diametersmaller than an inner diameter of said injection cylinder, saidinjection cylinder having an inner wall surface defining, jointly withan outer peripheral surface of said block, a clearance for accommodatinga residue of said molten metal matrix composite material.
 10. Aninjection apparatus as set forth in claim 9, wherein said block isdetachably secured to said plunger.
 11. An injection apparatus as setforth in claim 10, wherein said plunger has a head portion withprojection projecting upwardly, and said block has a recess provided ona lower surface thereof, so that said projection of said plunger can bedetachably fitted in said recess of said block.
 12. An injectionapparatus as set forth in claim 9, wherein said block is formed of amaterial harder than said metal matrix composite material aftersolidification.